[Sensory scaling of odor based on mathematical studies of rating words]

Sensory scales are very important indicators for the evaluation of environmental odors, and of the effect of deodorizers. The purpose of this study is to examine reasonable methods of sensory scaling. For this purpose, the psychological values of rating words for odor intensity, odor hedonics and similarity were measured. The interval distances between categories of each scale were estimated in the method of successive categories as well. Results of this study are as follows. 1) The 6-step odor intensity scale, issued by the Environmental Agency, may be regarded as an ordinal scale, but not as an interval scale. The 9-step hedonics scale may be regarded as an interval scale. 2) Psychological values of rating words are not affected by the size and the number of category steps in the graphic scales applied to the judgements of their values. 3) The number of category steps needs to be determined based on the distribution of the psychological values. The meanings and the order of the rating words have to be clear. 4) In the construction of a numerical scale, the category values should accord nearly as possible with the psychological values of rating words. 5) In results from the method of successive categories applied to the measured values of odor intensity and similarity, interval distances between categories are unequal, and the interval distances are wide on both edges of the scale. In these cases, the values must be converted into "category values of stimuli."